Loading...
1988 Speed Zone Surveyu A , Automobile Club of Southern California HEAOQUAAIEAS. 2601 SOUTH F I G U E A 0 A S I A E E I • LOS ANGELES, CALIFORNIA 90007329/ VIA ILIN G: P.0. AOI 2190 TERMINAL ANMEI • LOS ANGELES, CALIFORNIA 90051 0690 MKHWAY ENGINEERING DEPARTMENT A RUTH GRIM, MANAGER May 19, 1988 Mr. Frank Reynolds Director of Public Works/ City Engineer City of La Quinta P.O. Box 1504 La Quinta, CA 92253 Dear Mr. Reynolds: In response to your earlier request, we are pleased to submit the attached report on speed zones for the City of La Quinta. We wish to express our appreciation for the cooperation and assist- ance extended us by Roger Hirdler and Officer Darrell Czajkowski whose insights were important to the success of the study. If you have any questions about any of the recommendations contained in the report, please give us a call. Cordially, �i/ox*enGary Tr is Engineer bk a SPEED ZONE SURVEY FOR THE CITY OF LA QUINTA May 1988 BY THE Highway Engineering Department OF THE Automobile Club of Southern California AVe. 52, Bermudas, Tampico, Eisenhower, Jefferson and Washington SPEED ZONE SURVEY FOR THE CITY OF LA QUINTA INTRODUCTION a The Highway Engineering Department -of the Automobile Club of Southern California submits this report in response to a request from the City of La Quinta for assistance in the review of speed zones on 6 City streets described below. The purpose of the study was to deter- mine appropriate speed zones for these streets consistent with the requirements of California Vehicle Code Section 40802(b). Simply stated, the Vehicle Code requires that posted speed limits on the more important streets of a community be based upon a rational evaluation of roadway and roadside conditions, a review of the acci- dent history and measurements of prevailing speeds before radar can be used for their enforcement. STREETS SURVEYED The streets surveyed and limits of the study are shown on a map which is included in the "APPENDIX" section of this report and are described as follows: Avenue 52 - Avenida Bermudas to Adams Ball Field Avenida Bermudas - Calle Durango to Calle Madrid Calle Tampico - Washington Street to Eisenhower Drive Eisenhower Drive - Washington Street to Avenue 50 Eisenhower Drive - Calle Tampico to Avenida Bermudas Jefferson Street - Highway 111 to Westward Ho Drive Washington Street - Highway 111 to 3400 feet south STUDY PROCEDURE Nationally recognized study procedures, consistent with CVC Section 627 and the methods described in Chapter 8 of the California State Traffic Manual were followed in this study. Speed data were collected by City staff following a training exer- cise conducted by Auto Club representatives covering recognized pro- cedures. They recommend using a radar device in an unmarked car with the results being recorded on "Motor Vehicle Speed" forms (see "APPENDIX"). The data were fed into an Auto Club computer which pro- duced a printout of the various elements of speed discussed in the "ESTABLISHING SPEED ZONES" section which follows. A computer run was made for each survey location and those printouts are bound with the appropriate "Motor Vehicle Speed" forms in the "APPENDIX". -2- Acaitlonally, tre file of acciaents containEd fn the Statewide Integrated Traffic Records System was analyzed by the Auto Club for calendar years 1986 and 1987. Generally, accidents related to excessive speed were not a problem of significance but where excep- tions were noted, the speed related accident history was considered as an influence upon recommendations for posted speed limits. As a final element of the study, each street was driven in the presence of City staff to identify existing roadway and roadside conditions, and those observations in combination with the analysis of accidents, formed the basis for the improvement suggestions included in the "RECOMMENDATIONS" section of this report. ESTABLISHING SPEED ZONES The purpose of speed zoning is to establish realistic posted limits which aim to: • Encourage voluntary compliance by a majority of drivers. • Provide an enforcement tool that effectively separates the occasional violator from the reason- able majority. * Facilitate safe and orderly traffic flow . Two measurements extracted from the speed data are key to the estab- lishment of reasonable speed limits --the Prevailing speed and the Pace speed. The Prevailing speed is also known as the 85th percen- tile or critical speed. The Prevailing speed is that speed at or below which 85 percent of the observed vehicles were travelling. It is usually within 2 mph of the upper limit of the Pace. The Pace speed is the 10 mph range of speed which contains the greatest number of observed vehicles. Unless accident statistics or unexpected roadway conditions dictate otherwise, speed limits should be set at or near the Prevailing speed. The posted zone will normally coincide with the 5 mph increment next below the Prevailing speed (e.g. Prevailing speed = 38 mph, speed limit posting = 35 mph). A more detailed explanation of speed zoning principles and methods is contained in the "Speed Zoning, Why and How" booklet submitted with this report. DATA PRESENTATION Table 1 summarizes the speed data and shows the effects upon traffic of the recommended limits. The percent of traffic violating each existing speed limit is also noted. A high violation rate would indicate an unreasonable and not effectively enforceable speed limit, thereby leading to unjustifiable tolerances of 15 mph or more before I i^F:p NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F:q NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 It -3- enforcement action is applied. Cnanging to realistic speed IimiiitS would result in better driver compliance and would more clearly identify that segment of the driving population which legitimately deserves enforcement action without excessive tolerances. The view held by many, is that a 5 mph tolerance for speedometer and radar error is the most that can be justified. The Automobile Club of Southern California generally supports that enforcement philosophy, providing that speed zones are established according to prescribed practices. This is particularly true of zones which are posted at or within 2 mph of the prevailing speed where violations of 5 mph or more are so clearly out of line with the behavior of the average driver as to constitute a significant risk. Table 1 also includes a summary of the 2 year total number of acci- dents which have occurred on each of the roadways and, of the total, the number of collisions which were related to excessive speeds. Table 2 presents a more detailed look at accidents including their severity and the involvement of alcohol as well as the information mentioned above. The summary of accidents can be helpful in establish- ing enforcement and safety improvement priorities. RECOMMENDATIONS AVENUE 52 - Post a 50 mph speed limit between Adams Ball field and the curve west of Washington Street. The portion south and west of subject curve should be surveyed after road construction activities are completed and posted accordingly. • Place edge stripes throughout the entire section of road to more clearly define the travelled way. • Review the chevron alignment sign installations for both directions at the"S" curve east of Washington St. and the 900 curve west of Washing- ton Street. Three signs should be in the motorist's view as they travel through the curve (see page 4-34 of State Traffic Manual). AVENIDA BERMUDAS - Retain 45 mph speed limit posting. • Remove shrubbery within the right-of-way at Calle Sonora, Avenida Nogales and Avenida Chillon to improve visibility. • Review the chevron alignment sign installation at the curve south of Avenida Arroba to ensure compliance with the "3 signs in view" require- ment of the State Traffic Manual. • Stripe a double yellow centerline through the short tangent between the curves at Calle Madrid and Calle Chillon. U -4- CALLE 7hN,FiCO - post a 45 mp- speed ilt between, h&S,n!ny_. Street and Desert Club Drive and 35 mph between Desert Club Drive and Eisenhower Drive. • Install more prominent signs and markings to define the right -turn only lane into the new subdivision on the north side east of Avenida Bermudas. • Review the need for extending the double yellow centerline striping to the east from the Avenida Bermudas curve based upon passing sight distance requirements. EISENHOWER DRIVE - Retain 45 mph between Avenida Bermudas and Calle Durango, and between Avenue 50 and Washington Street. The speed data on the section between Avenue 50 and Washington Street would normally call for a posted limit of 50 mph and the majority of the roadway appears able to safely accommodate such speeds. However, there is a rather severe visibility restriction at the intersection of Eisenhower Drive and Coachella Drive, caused by a combination of factors (road curvature, narrow parkway and presence of a block wall), which cannot support a 50 mph approach speed. For this reason and because the survey section is not long enough for multiple speed zones, a 45 mph zone is recommended. The City has already taken steps to cope with the visibility restriction by modifying the roadway striping and delineation for eastbound traffic and by installing an advance intersec- tion warning sign with a flashing beacon. That has helped, but further improvements are desirable. Reportedly, discussions are underway for construction of a traffic signal at Coachella Drive and its completion should resolve the issue satisfactorily allowing, then, for a posted limit more in line with driver expectancy. In the interim, it is suggested that consideration be given to relocating the stop line on Coachella Drive 6-7 feet ahead of its present position in order to improve visibility to the maximum extent possible. Additional recommendations for this roadway are as follows: • Install "COACHELLA DRIVE" street name signs in advance of the intersection for both directions of travel. • Place appropriate arrow pavement markings to supplement the lane assignment signs controlling the 3 eastbound turn lanes at Washington Street. L -5- • Eliminate the rignt-turn cr:;j restri t��rs -.��s�c upon the westbound right lane at the first two intersections west of Washington Street. There is simply not enough right -turn demand to justify the restriction and the potential confusion it creates. Instead, allow the lane to be used by through traffic and, supplemented by appropriate sign- ing and arrow markings, terminate the lane markings far enough away from the point where the road narrows to allow adequate opportunity for traffic to merge. • Replace the existing "RIGHT TURN ONLY" sign for southbound traffic at Avenue 50 with a "RIGHT LANE MUST TURN RIGHT" sign positioned for better visibility. • Repaint the worn centerline markings between Avenida Bermudas and Calle Tampico. • Remove shrubbery within the right-of-way at Calle Sonora, Calle Ensenada and at Calle Temecula to improve visibility. JEFFERSON STREET - Post 40 mph between Highway 111 and Westward Ho Drive. • Remove "CAUTION" warning signs for both directions in advance of the marked golf cart crossing south of Westward Ho Drive and install more explicit W 54 pedestrian crossing symbol signs adjacent to the crossing. • Replace "END 35 ZONE" sign for northbound traf- fic north of Westward Ho Drive with an R3 "END 40 MPH SPEED LIMIT" sign. • Placean R2-4 "40 ZONE AHEAD" sign for south- bound traffic north of Westward Ho Drive. • Place "DIP" pavement markings along with W32 "DIP" warning signs and appropriate W6 advisory speed plates for both directions of travel in advance of the dip at the south side of Highway 111. WASHINGTON STREET - Post 45 mph from Highway 111 to 3400 feet south. While the speed data for this section of highway would normally support a posting of 50 mph, the roadside conditions and acci- dent record justifies a 45 mph limit. These roadside condi- tions include the presence of single family residences along the west side of the road, all with direct access, and the uw Eta need to zcck froi:. c"1veWajs c, -.-_o the nlyGwdy. ..,e c:.cident history also justifies the slight speed zone deviation with 59% of the accidents primarily caused by excessive speed. • With the help of Caltrans, immediately initiate a detailed investigation of accidents and road conditions at the Highway 111 intersection in an attempt to identify improvements which will help to reduce hazards at this accident prone intersection. The Auto Club would welcome the opportunity to participate in this study if our help is desired. • Install an R3 "END 45 SPEED LIMIT SIGN" for southbound traffic at the end of the desig- nated speed zone. CONCLUSIONS This report verifies or recommends establishment of speed zones that benefit all road users in LA QUINTA. The speed zones recommended will normally not increase operating speeds but rather adjust the law on the most important streets in the City to more closely reflect the reasonable actions of the majority of motorists. A look at the speed data will prove this point as most of the previously surveyed speed zones are still valid and need not be changed. City staff and law enforcement officers should continually review traffic operations to: • identify needed intersection and mid -block roadway improve- ments, • monitor accident trends, e review speed trends and make appropriate adjustments in speed limits and enforcement activity, • pursue educational and training opportunities. Finally, City Council action by resolution or ordinance will be needed for the legal establishment of all speed zones not covered by previous action. i^F:v NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F:w NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F:x NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F:y NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F:z NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02 i^F: NOTEXTPAGE BIB] 11-05-1998-U01 10:01:42AM-U01 BASIC-U01 CC-U02 06-U02 07-U02 1988-U02